Long-term plant community changes in restored and remnant Willamette valley wet prairie wetlands

Background/Question/Methods

Wet prairie wetlands are one of the rarest habitat types in the Willamette Valley of Oregon in today.  Less than one percent of their historic extent remains, with most having been converted into agricultural fields.  This habitat is the obligate or preferred habitat for multiple threatened or endangered plants.  Identification of remnant patches and restoration of prior patches is an ongoing effort. Still, little research into long-term changes in restored or remnant patches or effects of different management practices has been conducted. We sampled eight wet prairies, including four remnants and four restorations, in 2000, 2005, and 2011 using 100 m² Relevé plots to examine plant species richness and percent cover.  The eight sites are roughly grouped into four northern and four southern sites.  We then analyzed the trajectory of plant community change in these wetlands to assess the effects of time and management practices.  We used non-metric multidimensional scaling (NMDS) and multi-response permutation procedure (MRPP) to identify the trends in species assemblages at each site and the trajectories of change among all sites.

Results/Conclusions

Overall, the richest sites are located in the southern study area, with one remnant and one restoration in the southern study area as the two richest sites today.  We found that the four sites in the northern portion of the study area are becoming more similar over time as are the four sites in the southern portion of the study area.  Additionally, while geographic location is a statistically significant and biologically relevant grouping variable according to MRPP, the distinction between remnant and restored prairie is not.  The implications of different management practices including mowing, controlled burning, and hydrological alterations are currently being investigated and may help explain some of these trends.